Jul 01, 2002—July 1, 2002 - The inmate population in the United States is now just over 1.4 million, according to the Bureau of Justice Statistics. How do prisons keep track of all these criminals? The same way they have for decades: By counting heads five to eight times a day. That means when there is an escape, it often goes undetected until the next head count, which can give the prisoner valuable time to get away.

Calipatria prison

Technology Systems International (TSI), a Scottsdale, Ariz., company founded in 1994, would like to change that by using radio frequency identification to track inmates in real time, providing an early warning when someone attempts to break out. Calipatria State Prison, a maximum-security facility tucked in the desert in the southeast corner of California, has been testing the system since last October. It foiled at least one escape, identified prisoners involved in a riot and provided other benefits.

Here's how the system works. A transmitter, which looks like a large industrial wristwatch, is strapped to the wrist of each of Calipatria's 325 level-one (low-security) inmates. The device holds a 900 MHz RFID transmitter with a battery that sends out a signal every couple of seconds. The transmitter is housed in a tamperproof casing and strapped with screws with tamper-resistant covers. If the band is cut or a prisoner manages to slide the band off, an alarm is automatically triggered at a central monitoring station.

Readers with antennas are set up around the prison yard and throughout the interior of the building. Calipatria has about 60 readers, which pick up signals from every transmitter in the facility. At least three readers may pick up a signal from each inmate, but its usually many more to provide redundancy in the system. The signals are sent to a collector node, which calculates the person's location to within a few feet and puts a time of arrival stamp on the information and forwards it to computers running TSI's control software, which is used to establish the conditions for alerts. The system can handle up to 24,000 units, according to TSI. The readers can process hundreds of signals virtually simultaneous, because the signals are transmitted up so quickly.

Prisons set up the system to alert the central station monitor when inmates leave their authorized area, which is scheduled by time. That prevents them from orchestrating escapes or other crimes within the prison. Escapes are normally detected when the inmate removes or destroys his tag, which sets of an alert either instantly, or within one minute.

The software can be programmed to alert the central station when an inmate wanders into an area where he doesn't belong, or when he fails to return from a furlough at the appropriate time. If a prison has a problem with gangs, the system can send out an alert when two members from rival gangs come within, say, 15 feet of one another. Male and female prisoners can be kept apart this way as well.

Each correctional officer also wears a transmitter, which looks like a pager with a big red emergency button in it, strapped to his or her belt. If a guard feels threatened by inmates, he can push the button on his transmitter. The system immediately identifies the guard and his location. It also identifies the 20 inmates closest to him and the closest officers who can respond, so help can be dispatched.

The system tracks the movements of everyone in real time, so if the guard is taken to another area, prison officials can see exactly he is and which prisoners are holding him. "The system takes away the veil of secrecy and gives power back to the guards," says TSI President Greg Oester.